Material for electronic device and process for producing the same

ABSTRACT

An electronic device material comprising at least an electronic device substrate and a silicon oxynitride film disposed on the substrate is provided. The silicon oxynitride film is characterized by containing nitrogen atoms in a large amount in the vicinity of the oxynitride film surface when the nitrogen content distribution in the thickness direction of the silicon oxynitride film is examined by SIMS (secondary ion mass spectrometry) analysis. By virtue of this constitution, an electronic device material comprising an oxynitride film having an excellent effect of preventing penetration of boron and having excellent gate leak properties can be obtained.

TECHNICAL FIELD

The present invention relates to an electronic device material having anoxynitride film excellent in various properties (for example, barrierproperty to boron), and a production process thereof. The electronicdevice material and its production process of the present invention canbe suitably used, for example, for forming a material for semiconductorsor semiconductor devices (for example, those having an MOS-typetransistor structure with a gate insulating film having excellentproperties).

BACKGROUND ART

The present invention is widely applicable to the production in generalof a material for semiconductors or electronic devices such assemiconductor device and liquid crystal device, but for the sake ofconvenience, the background art of semiconductor devices is describedhere as an example.

With recent miniaturization of semiconductor devices, needs for a thinand good-quality silicon oxide film (SiO₂ film) are significantlyincreasing. For example, in an MOS-type transistor structure (FIG. 1)which is a most popular constitution of semiconductor devices, a verythin (for example, about 2.5 nm or less) and good-quality gateinsulating film (SiO₂ film) according to the so-called scaling rule iskeenly demanded.

The gate insulating film material heretofore used in industry is asilicon oxide film (SiO₂ film) obtained by directly oxidizing a siliconsubstrate in a high-temperature heating furnace of approximately from850 to 1,000° C.

However, if such an SiO₂ film is merely made thin to 2.5 nm or less, theleak current passing through the gate insulating film (gate leakcurrent) becomes large and this causes problems such as increase ofpower consumption or accelerated deterioration of device properties.

Furthermore, in using a conventional thin gate insulating film, boroncontained in a gate electrode (mainly polysilicon) of a P-type MOStransistor penetrates into the SiO₂ film at the formation of the gateelectrode and the boron concentration of the gate electrode changes tocause a problem that the semiconductor device properties deteriorate. Asone of the methods for solving such problems, studies are being made touse an oxynitride film (acid nitride film) as the gate insulating filmmaterial.

When nitrogen is contained in the insulating film, this is advantageousin that the dielectric constant of the film is elevated and theelectrical capacitance (capacitance) increases as compared with an oxidefilm having the same physical film thickness. The MOS-type transistor,which can be typically represented by the structure shown in FIG. 1described later, contains an MOS (metal-oxide-semiconductor) capacitorstructure using a gate insulating film as the dielectric material,between two metals (doped polysilicon (gate electrode) and siliconsubstrate).

In order to attain high-speed transistor operation, the time requiredfor a carrier to move between the source and the drain shown in FIG. 1must be shortened. The measure therefor includes two approaches, thatis, a method of increasing the speed (mobility) of the carrier movingbetween the source and the drain, and a method of reducing the distancebetween the source and the drain. At present, the control of theinterface between the silicon substrate and the oxide film reaches thelimit and the mobility can be hardly increased any more.

Accordingly, the method of reducing the channel length in the MOSstructure of FIG. 1 is used at present for achieving high-speedoperation of transistor. As this channel length is shorter, the timerequired for a carrier to move becomes shorter and a transistoroperation at a higher speed can be realized. However, the reduction ofthe channel length has the same meaning as the reduction in the area ofMOS capacitor contained in that portion, namely, reduction in thecapacitance, and this gives rise to an insufficient amount of carrier(electron or hole) induced at the operation and in turn, difficulty inobtaining an S/N ratio high enough to bring about the operation.Accordingly, in order to realize a device having high-speed operationreliability, a measure must be taken to maintain the capacitance evenwhen the area is decreased.

As the measure therefor, a method of decreasing the film thickness ofthe gate insulating film of FIG. 1 has been conventionally employed, butthe thinning of the film incurs the following problems. One problem isthat a current (leak current) flows between the silicon substrate(channel) and the gate electrode due to quantum mechanical tunnel effectand the power consumption increases. A low power consumption device isessential for the development of portable electronic devices in arecently started ubiquitous society (information society allowing forconnection to the network at any time and any place through anelectronic device as the medium), and reduction of this leak current isan important problem.

Also, with the thinning of the gate oxide film, as described above, thepenetration of boron from the gate electrode of a P-type MOS transistorcomes out as a serious problem. Boron has a property of readily passingthrough an oxide film and as the film is more thinned, this causes aproblem that boron penetrates the oxide film and the boron concentration(dope amount) of the gate electrode changes. A CMOS structure(mixed-mounting of N-type and P-type transistors) is fundamental for lowpower consumption devices and accordingly, the presence of a P-type MOStransistor is indispensable. The change in the dope amount of the gateelectrode causes change in the threshold voltage of the transistor andthe transistor may undergo irregular operation. Therefore, it is veryimportant to prevent the penetration of boron.

In order to solve these problems, as described above, a method ofincorporating nitrogen into the silicon oxide film has been proposed.When nitrogen contained, this is known to elevate the dielectricconstant and prevent the penetration of boron.

However, if such an oxynitride film is directly and simply formed by athermal oxynitridation method, nitrogen is contained in a large amountat the interface with the silicon substrate and the device propertiesinevitably tend to be deteriorated. When nitrogen is contained at theinterface, this is known to cause deterioration in the mobility ofcarrier and in turn in the transistor operation properties. Also, in anSiO₂/SiN stack structure combining the formation of thermal oxide filmand the formation of SiN film by CVD (chemical vapor deposition), a trap(in-film level) of carrier is generated at the SiO₂/SiN interface andthis tends to cause deterioration of the device properties, such asshifting of the threshold voltage.

When the SiO₂ film is intended to nitride by heating, a high temperatureof 1,000° C. or more is usually necessary and in this heat step,differential diffusion of the dopant injected into the silicon substrateis liable to occur to deteriorate the device properties (such a methodis disclosed in Japanese Unexamined Patent Publication (Kokai) Nos.55-134937 and 59-4059).

DISCLOSURE OF THE INVENTION

An object of the present invention to overcome those problems inconventional techniques and provide an electronic device materialcomprising an oxynitride film having excellent properties (for example,excellent barrier property to boron), and a production process thereof.

Another object of the present invention is to provide an electronicdevice material comprising an oxynitride film formed to have goodinterface property (high mobility) by controlling the nitrogen contentat the interface between the substrate and the oxynitride film andprevented from in-film level in the oxynitride film, and a productionprocess thereof.

As a result of intensive investigations, the present inventors havefound that when nitrogen on an electronic device substrate is disposedin the vicinity of a silicon oxynitride film surface in the nitrogencontent distribution based on SIMS (secondary ion mass spectrometry)analysis, this is very effective for achieving the above-describedobjects.

The electronic device material of the present invention is accomplishedbased on this finding. More specifically, the electronic device materialof the present invention is characterized by comprising at least anelectronic device substrate and a silicon oxynitride film disposed onthe substrate, wherein the silicon oxynitride film contains nitrogenatoms in a large amount in the vicinity of the surface when the nitrogencontent distribution in the thickness direction of the siliconoxynitride film is examined by the SIMS (secondary ion massspectrometry) analysis.

The present invention further provides a process for producing anelectronic device material, comprising irradiating a plasma based on aprocess gas containing at least a nitrogen gas on a silicon oxide filmdisposed on an electronic device substrate, thereby forming a siliconoxynitride film containing nitrogen atoms in a large amount in thevicinity of the surface when the nitrogen content distribution in thethickness direction of the silicon oxynitride film is examined by theSIMS (secondary ion mass spectrometry) analysis.

The electronic device material constituted as above of the presentinvention can have excellent properties (for example, barrier propertyto boron) by virtue of a high N-atom concentration portion formed in thesilicon oxynitride film constituting the electronic device material andalso, can be prevented from deterioration of properties (for example,mobility) at the interface of silicon oxynitride film/electronic devicesubstrate by virtue of the presence of a low N-atom concentrationportion in the nitrogen content distribution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing one example of theMOS structure which can be formed by the present invention.

FIG. 2 is a schematic cross-sectional view showing one example of thesemiconductor device which can be produced by the production process ofan electronic device material of the present invention.

FIG. 3 is a schematic plan view showing one example of the apparatus forproducing a semiconductor, which is used for practicing the productionprocess of an electronic device material of the present invention.

FIG. 4 is a schematic vertical cross-sectional view showing one exampleof the plane antenna (RLSA; sometimes called a slot plane antenna orSPA) plasma treatment unit which can be used in the production processof an electronic device material of the present invention.

FIG. 5 is a schematic plan view showing one example of RLSA which can beused in the production apparatus of an electronic device material of thepresent invention.

FIG. 6 is a schematic vertical cross-sectional view showing one exampleof the heating reaction furnace unit which can be used in the productionprocess of an electronic device material of the present invention.

FIGS. 7 and 8 each is a flow chart showing one example of each processin the production process of the present invention.

FIG. 9 is a graph showing the SIMS analysis results of the oxynitridefilm obtained in Example.

FIG. 10 is a graph showing the SIMS analysis results of the oxynitridefilm obtained in Example.

FIG. 11 is a graph showing the SIMS analysis results of the oxynitridefilm obtained in Example.

FIG. 12 is a graph showing the SIMS analysis results of the oxynitridefilm obtained in Example.

FIG. 13 is a graph showing the results in the boron penetration test ofthe oxynitride film obtained in Example.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in detail below by referring to thedrawings as needed. In the following, unless otherwise indicated, the“parts” and “%” showing the amount ratio are based on the mass.

(Electronic Device Material)

The electronic device material of the present invention comprises atleast an electronic device substrate and a silicon oxynitride (SiON)film disposed on the substrate. In the present invention, the siliconoxynitride film has, in its thickness direction, a nitrogen contentdistribution based on the SIMS (secondary ion mass spectrometry)analysis.

(Electronic Device Substrate)

The electronic device substrate which can be used in the presentinvention is not particularly limited, and one or a combination of twoor more appropriately selected from known electronic device substratescan be used. Examples of the electronic device substrate includesemiconductor materials and liquid crystal device materials. Examples ofthe semiconductor material include a material mainly comprising singlecrystal silicon and a material mainly comprising silicon germanium, andexamples of the liquid crystal device material include polysilicon andamorphous silicon formed on a glass substrate.

(Silicon Oxynitride Film)

In the present invention, the silicon oxynitride film is notparticularly limited in the composition, shape, layer thickness,nitrogen atom distribution in layer (distribution) and the like as longas the silicon oxynitride film has a nitrogen content distribution basedon the SIMS (secondary ion mass spectrometry) analysis. In the presentinvention, from the standpoint of preventing diffusion of a dopant(boron) in a P-type transistor, the nitrogen content is preferably 10%or more, more preferably 20% or more. On the other hand, from thestandpoint of enhancing the dielectric constant, the nitrogen content ispreferably from 20 to 40%. If the nitrogen content is too small, theeffect of enhancing the dielectric constant is low, whereas if it isexcessively high, nitrogen highly probably reaches the interface todeteriorate the carrier property (mobility) and the like at theinterface. In general, it is known that the dielectric constant ofsilicon oxide film (SiO₂) is 3.9 and the dielectric constant of siliconnitride film (Si₃N₄) is 7. Accordingly, in the case of oxynitride filmwhere the ratio of oxide film mixed is purely 1:0.2, the dielectricconstant of the oxynitride film is (3.9×1+7×0.2)÷(1+0.2)=4.1. When thisoxynitride film is used, a film having a thickness as large as4.1÷3.9=1.1 times as compared with the oxide film can be physicallyformed, but with such a film thickness, the effect of decreasing thepower consumption by the enhancement of dielectric constant isinsufficient. Therefore, a higher nitrogen content is more preferred.Conversely, if too high, a large amount of nitrogen is contained at thesilicon substrate-oxide film interface to significantly deteriorate theproperties at the interface (for example, deterioration of mobility) andthis cancels the merit obtained by the thinning of film (high-speedoperation by the reduction in the distance between source and drain).From these reasons, the nitrogen content is preferably controlled to aproper value.

The nitrogen content can be suitably measured by the SIMS (secondary ionmass spectrometry) method. Preferred conditions at this measurement ofnitrogen content are shown below.

<Preferred Conditions for Nitrogen Content Measurement>

-   Measuring apparatus: Physical Electronics 6650-   Primary ion species: Cs+-   Primary acceleration voltage: 0.75 KV-   Sputtering rate: about 9E-3 nm/sec-   Measurement region: diameter 420 μm×672 μm-   Degree of vacuum: 3E-7 Pa or less-   Measured ion polarity: +-   Charge-up compensation process: employed

The signal intensity of ion is converted into the concentration with useof a relative sensitivity factor (RSF) determined by measuring an SiO₂standard sample in which N is ion-injected. Also, the sputtering time isconverted into the depth by measuring the depth of a crater generatedupon analysis with use of a surface roughness meter (DEKTAK8000,manufactured by SLOAN).

(Nitrogen Atom Distribution)

In the present invention, from the standpoint of preventing penetrationof boron or the like and making a good balance with the interface levelat the oxynitride film/substrate interface, the half-width of thenitrogen atom distribution curve (profile) in the oxynitride film ispreferably 2 nm or less, more preferably 1.5 nm or less, still morepreferably 1 nm or less.

In view of the above-described good balance with the interface level atthe oxynitride film/substrate interface, the oxynitride film, for use inthe present invention preferably further has one or more properties of(1) to (3) below.

(1) The maximum value N_(s) of the nitrogen atom content (atm %) in therange of 0 to 1.5 nm from the oxynitride film surface side (that is, asurface of the oxynitride film opposite the surface facing thesubstrate) is preferably from 10 to 30 atm %, more preferably from 20 to30 atm %.

(2) The maximum value Nb of the nitrogen atom content (atm %) in therange of 0 to 0.5 nm from the oxynitride film surface facing thesubstrate is preferably from 0 to 10 atm %, more preferably from 0 to 5atm %.

(3) The ratio N_(s)/N_(b) of N_(s) and N_(b) is preferably 2 or more,more preferably 3 or more, still more preferably 4 or more.

(Production Method of Electronic Device Material)

The electronic device material having such a constitution of the presentinvention is not particularly limited in its production process, butfrom the standpoint of ensuring a high nitrogen content and preventingthe channel dopant from diffusing due to low heat history, a method ofirradiating the silicon oxide film disposed on the electronic devicesubstrate with a plasma based on a process gas containing at least anitrogen gas is preferred.

When a plasma is used for the formation of oxynitride film of thepresent invention, this is advantageous in that the nitridation can beperformed at a low temperature as compared with thermal nitridation andthe channel dopant can be prevented from diffusing. Furthermore,nitridation of the SiO₂ film with use of a plasma is advantageous inthat generally, a high-quality oxynitride film (for example, gateoxynitride film) reduced in the in-film level is readily obtained ascompared with the case of forming a nitride film on an SiO₂ film by theCVD method.

(Treating Gas)

The process gas which can be used in the present invention is notparticularly limited as long as it contains at least a nitrogen gas, andone or a combination of two or more appropriately selected from knownprocess gases usable for the production of an electronic device can beused. Examples of the process gas include a mixed gas containing a raregas and nitrogen (N₂).

(Rare Gas)

The rare gas which can be used in the present invention is notparticularly limited and one or a combination of two or moreappropriately selected from known rare gases usable for the productionof an electronic device can be used. Examples of this process gasinclude krypton (Kr), xenon (Xe), helium (He), neon (Ne) and argon (Ar).

(Treating Gas Conditions)

In the production of oxynitride film of the present invention, in viewof properties of the oxynitride film to be formed, the followingconditions are preferably employed.

-   Rare gas (e.g., Kr, Ar, He, Xe):    -   from 500 to 3,000 sccm, more preferably    -   from 1,000 to 2,000 sccm-   N₂: from 2 to 500 sccm, more preferably    -   from 4 to 300 sccm-   Temperature: from 25° C. (room temperature) to 500° C.,    -   more preferably from 250 to 500° C.,    -   still more preferably from 250 to 400° C.-   Pressure: from 3 to 260 Pa, more preferably    -   from 7 to 260 Pa, still more preferably from 7 to 130 Pa-   Microwave: from 0.7 to 4.2 W/cm², more preferably    -   from 1.4 to 4.2 W/cm², still more preferably from 1.4 to 2.8        W/cm²        (Plane Antenna Member)

In the production process of an electronic device material of thepresent invention, when a microwave is irradiated through a planeantenna member having multiple slots, high-density plasmas having a lowelectron temperature can be formed in a large area with good uniformity.In the present invention, the oxynitride film is formed by using aplasma having such excellent properties and therefore, a low-temperatureand highly reactive process with small plasma damage can be obtained.

(Preferred Plasma)

The properties of the plasma which can be preferably used in the presentinvention are as follows.

-   Electron temperature: 0.5-2.0 eV-   Density: from 1E10 to 5E12/cm³-   Uniformity of plasma density: ±10%

According to the present invention, a good-quality oxynitride film canbe formed. Therefore, by forming another layer (for example, electrodelayer) on this oxynitride film, a semiconductor device structure havingexcellent properties can be easily fabricated.

(Preferred Properties of Oxynitride Film)

According to the present invention, an oxynitride film having thefollowing preferred properties can be easily formed.

-   Electrical film thickness (equivalent film thickness):    -   from 1.0 to 2.5 nm-   Leak properties:    -   reduced by a half to one digit as compared with Dry Ox-   Uniformity of film thickness: ±2%    (Preferred Properties of Oxynitride Film)

The method of the present invention is not particularly limited in itsapplication range, but the good-quality oxynitride film which can beformed by the present invention can be preferably used in particular asa gate insulating film of an MOS structure.

(Preferred Properties of MOS Semiconductor Structure)

The very thin and good-quality oxynitride film which can be formed bythe present invention can be preferably used in particular as aninsulating film (particularly, a gate insulating film of an MOSsemiconductor structure) of a semiconductor device.

According to the present invention, an MOS semiconductor structurehaving preferred properties as described later can be easily produced.Incidentally, in evaluating the properties of the oxynitride film formedby the present invention, for example, a standard MOS semiconductorstructure described in publications (see, Oyo Butsuri (Applied Physics),Vol. 69, No. 9, pp. 1049-1059 (2000)) is formed and by evaluating theproperties of the MOS, the properties of the oxynitride film itself canbe evaluated, because in such a standard MOS structure, the propertiesof the oxynitride film constituting the structure strongly affect theMOS properties.

(One Embodiment of Production Apparatus)

One preferred embodiment of the production process of the presentinvention is described below.

First, one example of the structure of a semiconductor device which canbe produced by the production process of an electronic device materialof the present invention is described by referring to FIG. 2 where thesemiconductor device has an MOS structure using a gate insulating filmas the insulating film.

Referring to FIG. 2( a), the reference numeral 1 in FIG. 2( a) is asilicon substrate, 11 is a field oxide film, 2 is a gate insulating filmand 13 is a gate electrode. As described above, according to theproduction process of the present invention, a very thin andgood-quality gate insulating film 2 can be formed. The gate insulatingfilm 2 comprises, as shown in FIG. 2( b), a high-quality insulating filmformed at the interface with the silicon substrate 1. For example, thegate insulating film is constituted by an oxide film 2 having athickness of about 2.5 nm.

In this example, the high-quality oxide film 2 preferably comprises asilicon oxide film (hereinafter referred to as “SiO₂ film”) formed on asubstrate surface by using plasmas generated resulting from irradiationof a microwave on the substrate to be treated, which mainly comprisesSi, through a plane antenna member having multiple slots in the presenceof a process gas containing O₂ and a rare gas. When such an SiO₂ film isused, as described later, good interface properties (for example,interface level) can be easily obtained and an MOS structure fabricatedcan have good gate leak property.

In the present invention, the surface of the silicon oxide film 2 ispreferably subjected to the above-described nitridation treatment. Onthe nitridation-treated surface of this silicon oxide film 2, a gateelectrode 13 mainly comprising silicon (polysilicon or amorphoussilicon) is further formed.

(Embodiment of Formation of Insulating Film)

One preferred example of the method for forming an insulating filmcomprising the gate insulating film 2 on a wafer W by using theabove-described apparatus is described below.

FIG. 7 is a view showing one example of each step in the method of thepresent invention.

Referring to FIG. 7, a field oxide film channel implant working out todevice separation and a sacrificial oxide film are formed on the wafer Wsurface in the step of A. In the step of B, the sacrificial oxide filmis removed.

Thereafter, a gate valve (not shown) provided on the side wall of avacuum container 50 in a plasma treatment unit 32 is opened and thewafer W after the removal of sacrificial oxide film is set on the table5 by using transportation arms 37 and 38 (see, FIG. 4).

Subsequently, after the gate valve is turned off to close the inside,the interior atmosphere is evacuated through an exhaust pipe 53 by avacuum pump 55 to a predetermined degree of vacuum, and a predeterminedpressure is maintained. Separately, a microwave of, for example, 2 W/cm²is generated from a microwave power supply 61 and this microwave isguided by a wave-guide path and introduced into the vacuum container 50through RLSA 60 and a top plate 54, whereby high-frequency plasmas aregenerated in the plasma region P on the upper side in the vacuumcontainer 50.

Here, the microwave is transmitted in a rectangular mode through arectangular wave-guide tube 63D, converted from a rectangular mode intoa circular mode by a coaxial wave-guide converter 63C, then transmittedin a circular mode through a cylindrical coaxial wave-guide tube 63B,further transmitted to the diameter direction through a plate-likewave-guide path 63A, radiated by slots 60 a of RLSA60 and introducedinto the vacuum container 50 through the top plate 54. At this time,high-density plasmas having a low electron temperature are generatedbecause of use of a microwave and also, plasmas are uniformlydistributed because the microwave is radiated through many slots 60 a ofRLSA60.

Thereafter, while heating the wafer W, for example, at 400° C. bycontrolling the table 52 temperature, a rare gas such as krypton orargon and an O₂ gas, which are the process gas for the formation ofoxide film, are introduced from a gas supply tube 72 at a flow rate of2,000 sccm and 200 sccm, respectively, to practice the step C (formationof oxide film).

In this step C, the process gas introduced is activated (formed intoradicals) by a plasma flow generated in the plasma treatment unit 32and, as shown in the schematic cross-sectional view of FIG. 8( a), thesilicon substrate 1 surface is oxidized under the action of the plasmasto form an oxide film (SiO₂ film) 2.

This oxidation treatment is performed, for example, for 40 seconds,whereby a 2.5 nm-thick gate oxide film or underlying oxide film(underlying SiO₂ film) 21 for gate oxynitride film can be formed.

Subsequently, the gate valve (not shown) is opened and transportationarms 37 and 38 (see, FIG. 3) are caused to proceed into the vacuumcontainer 50 and receive the wafer W on the table 52. The transportationarms 37 and 38 take out the wafer W from the plasma treatment unit 32and then set it on the table of an adjacent plasma treatment unit 33(step 2). Depending on use, the gate oxide film is sometimes moved to aheating reaction furnace 47 without being nitrided.

(Embodiment of Nitride-Containing Layer Formation)

Thereafter, a surface nitridation treatment is applied to the wafer W inthe plasma treatment unit 33 (see, FIG. 7( c)), and a nitride-containinglayer 22 (see, FIG. 8( b)) is formed on the surface of the previouslyformed underlying oxide film (underlying SiO₂) 21.

At this surface nitridation treatment, the inside of, for example, avacuum container 50 is in such a condition that the wafer temperatureis, for example, 400° C. and the process pressure is, for example, 66.7Pa (500 mTorr), and an argon gas and an N₂ gas are introduced into thecontainer 50 from a gas inlet tube at a flow rate of 1,000 sccm and 40sccm, respectively.

Separately, a microwave of, for example, 2 W/cm² is generated from amicrowave power supply 61 and this microwave is guided by a wave-guidepath and introduced into the vacuum container 50 through RLSA 60 b and atop plate 54, whereby high-frequency plasmas are generated in the plasmaregion P on the upper side in the vacuum container 50.

In this step (surface nitridation), the gas introduced is plasmatized toform nitrogen radicals and the formed nitrogen radical reacts on theSiO₂ film formed on the upper surface of the wafer W, whereby the SiO₂film surface is nitrided within a relatively short time. In this way, asshown in FIG. 8( b), a nitrogen-containing layer 22 is formed on thesurface of the underlying oxide film (underlying SiO₂ film) 21 on thewafer W.

By performing this nitridation treatment, for example, for 20 seconds, agate oxynitride film (acid nitride film) having a thickness of about 2nm in terms of equivalent film thickness can be formed.

(Embodiment of Gate Electrode Formation)

On the wafer W having formed thereon the SiO₂ film or the oxynitridefilm resulting from nitridation of the underlying SiO₂ film, a gateelectrode (see, FIG. 7E(a); 13 of FIG. 2) is formed. In the formation ofthis gate electrode 13, the wafer having formed thereon the gate oxidefilm or gate oxynitride film is taken out from the plasma treatment unit32 or 33, respectively, and after once taken out to the transportationchamber 31 (see, FIG. 3) side, housed in the heating reaction furnace 47(step 4). In the heating reaction furnace 47, the wafer W is heatedunder predetermined treatment conditions to form a predetermined gateelectrode 13 on the gate oxide film or gate oxynitride film.

At this time, the treatment conditions can be selected according to thekind of the gate electrode 13 formed.

More specifically, in the case of forming a gate electrode 13 comprisingpolysilicon, the treatment is preformed by using, for example, SiH₄ asthe process gas (electrode-forming gas) under the conditions such thatthe pressure is from 20 to 33 Pa (from 150 to 250 mTorr) and thetemperature is from 570 to 630° C.

In the case of forming a gate electrode 13 comprising amorphous silicon,the treatment is preformed by using, for example, SiH₄ as the processgas (electrode-forming gas) under the conditions such that the pressureis from 20 to 67 Pa (from 150 to 500 mtorr) and the temperature is from520 to 570° C.

Furthermore, in the case of forming a gate electrode 13 comprising SiGe,the treatment is performed by using, for example, a mixed gas ofGeH₄/SiH₄=10/90 to 60/40% under the conditions such that the pressure isfrom 20 to 60 Pa and the temperature is from 460 to 560° C. Thereafter,patterning and etching of the gate electrode are performed (see, FIG.7F), the source and drain are formed (see, FIG. 7G) and a wiring step isperformed (see, FIG. 7H), whereby a e-type MOS transistor is formed.

(Quality of Oxide Film)

In the above-described first step, at the formation of gate oxide filmor underlying oxide film for gate oxynitride film, plasmas containingoxygen (O₂) and a rare gas are formed by irradiating a microwave on thewafer W mainly comprising Si through a plane antenna member (RLSA)having many slots in the presence of the process gas and by using theplasmas formed, an oxide film is formed on a surface of the substrate tobe treated, so that the oxide film can have high quality and the filmquality can be successfully controlled.

(Presumed Mechanism of High-Quality Oxynitride Film)

Also, the oxynitride film obtained by performing a surface nitridationtreatment in the above-described second step has an excellent quality.According to the knowledge of the present inventors, the reasonstherefor are presumed as follows.

The nitrogen radicals produced on the oxide film surface by RLSA are ina high density and therefore, nitrogen can be mixed into the oxide filmsurface in a unit of percent. Also, as compared with production ofnitrogen radicals by heat, high-density nitrogen radicals can beproduced even at a low temperature (about 300° C.) and therefore, thedevice properties can be prevented from deterioration due to heat asrepresented by diffusion or the like of dopant. Furthermore, sincenitrogen in the film is contained in the oxide film surface, it ispossible to enhance the dielectric constant and exert the performancesuch as effect of preventing penetration of boron without deterioratingthe interface properties,

(Presumed Mechanism of Preferred MOS Properties)

In the above-described third step, a gate electrode obtained by applyinga heat treatment under specific conditions is formed and thereby, anMOS-type semiconductor structure having excellent properties isfabricated. According to the knowledge of the present inventors, thereasons therefor are presumed as follows.

In the present invention, as describe above, a very thin andgood-quality gate insulating film can be formed. By combining such agood-quality gate insulating film (gate oxide film and/or gateoxynitride film) with a gate electrode (for example, polysilicon,amorphous silicon or SiGe by CVD) formed thereon, good transistorproperties (for example, good interface properties) can be realized.

Furthermore, by establishing a cluster system shown in FIG. 3, exposureto air can be prevented from occurring between the formation of gateoxide film or gate oxynitride film and the formation of gate electrode,and the interface properties can be more enhanced.

The present invention is described in greater detail below by referringto Examples.

EXAMPLES Example 1

The oxynitride film subjected to evaluation described later was producedthrough the following steps (1) to (7).

-   (1) Substrate

A 20-cm (8-inch) P-type or N-type silicon substrate having a resistivityof 8 to 12 Ωcm and a plane direction of (100) was used for thesubstrate.

-   (2) Washing before Gate Oxidation

A natural oxide film and contaminant factors (metal, organic materialand particle) were removed by RCA washing where APM (a mixed solution ofammonia:aqueous hydrogen peroxide:pure water=1:2:10, 60° C.), HPM (amixed solution of hydrochloric acid:aqueous hydrogen peroxide:purewater=1:1:10, 60° C.) and DHF (a mixed solution of hydrofluoricacid:pure water=1:100, 23° C.) were combined. In the RCA washing, APM:10 minutes→pure water rinsing: 10 minutes→DHF: 3 minutes→pure waterrinsing: 10 minutes→HPM: 10 minutes→pure water rinsing: 10 minutes→finalpure water rinsing: 5 minutes were performed and thereafter, IPA(isopropyl alcohol, 220° C.) drying was performed for 15 minutes to drythe water content on the wafer.

-   (3) Oxidation Process

On the silicon substrate treated in (2) above, an oxide film was formedby the following method.

That is, the silicon substrate treated in (2) above was carried into areaction chamber heated to 300° C. at an atmospheric pressure. After thewafer was carried in, a nitrogen gas was introduced at 5 slm and thepressure was kept at 0.7 KPa. In this atmosphere, the wafer was heatedat 850° C. and after the temperature was stabilized, an oxygen gas and ahydrogen gas were introduced at 0.7 slm and 0.1 slm, respectively. Inthis state, the silicon substrate was held for 3 minutes, whereby athermal oxide film of 2 nm was formed. After this oxidation treatment,in an atmosphere where a nitrogen gas was introduced at 3 slm, thetemperature was dropped to 300° C., the reaction chamber was returned toan atmospheric pressure, and then the wafer was carried out.

-   (4) Plasma Nitridation Process

The oxide film after the treatment in (3) above was subjected tonitridation. In this plasma nitridation process, a plasma device systemshown in FIG. 4 was used.

That is, in the plasma device system, an Ar gas and a nitrogen gas werepassed on the silicon substrate heated at 250° C. or 400° C., at 1,000sccm and 40 sccm, respectively, and the pressure was kept at 6.7 Pa or67 Pa (50 mTorr or 500 mTorr). In this atmosphere, a microwave of 3W/cm² was irradiated through a plane antenna member (RLSA) havingmultiple slots to form plasmas containing nitrogen gas and argon gas andby using the plasmas formed, the oxide film was nitrided to form anoxynitride film (acid nitride film). The evaluations shown in FIGS. 9 to12 were performed by using a sample treated until this step (4).

-   (5) Penetration of Boron

For evaluating the penetration of boron, a polysilicon film was furtherformed on the oxynitride film after the treatment in (4).

More specifically, the silicon substrate subjected to the treatment of(4) was heated to 630° C., a silane gas (SiH₄) was introduced onto thesubstrate at 250 sccm, and the pressure was kept at 33 Pa (250 mTorr)for 31 minutes, whereby a polysilicon film having a thickness of 300 nmwas formed. On this polysilicon, boron was injected by ion implantation.The injection conditions were such that the density was 5E15 [5×10¹⁵atms/cm²] and the injection energy was 5 KeV. The boron ion implanteddoes not play as is the role of a dopant (impurity) in the film and mustbe thermally annealed to accelerate its chemical combining with thesilicon atom in the polysilicon. The thermal annealing was performed byan RTA (rapid thermal annealing) treatment of heating the wafer at ahigh speed to 1,000° C. under an atmospheric pressure where nitrogen wasintroduced at 2,000 sccm, and keeping the wafer at the high temperaturefor 10 seconds.

Example 2

Samples treated until the step (4) above in Example 1 each was subjectedto SIMS analysis to evaluate the nitrogen content in film. At the sametime, the oxygen and silicon element were analyzed and from theseresults, the nitridation reaction was examined.

FIGS. 9 to 13 each shows the secondary ion mass spectrometry (SIMS)results of nitrogen atom when the thermal oxide film is subjected to thenitridation plasma treatment. The abscissa denotes the film thicknessand the ordinate denotes the nitrogen content. The SIMS conditions usedhere were as follows.

<SIMS Conditions>

-   Measuring apparatus: Physical-Electronics 6650-   Primary ion species: Cs+-   Primary acceleration voltage: 0.75 KV-   Sputtering rate: about 9E-3 nm/sec-   Measurement region: diameter 420 μm×672 μm-   Degree of vacuum: 3E-7 Pa or less-   Measured ion polarity: +-   Charge-up compensation process: employed

The signal intensity of ion was converted into the concentration withuse of a relative sensitivity factor (RSF) determined by measuring anSiQ₂ standard sample in which N was ion-injected. Also, the sputteringtime was converted into the depth by measuring the depth of a cratergenerated upon analysis with use of a surface roughness meter(DEKTAK8000, manufactured by SLOAN). However, in this measurement, theanalysis region was very shallow and the depth could be hardly measuredby the surface roughness meter. Therefore, the conversion into the depthwas performed by using a sputter rate obtained from a standard samplewhich was measured under the same conditions as each sample.

As shown in FIGS. 9 and 11, when the method for forming an oxynitridefilm of the present invention was used, nitrogen could be successfullycontained in the film to account for from 15 to 30%. Also, as shown inFIG. 13 which is described later, the penetration of boron could beprevented by applying a nitridation treatment.

FIG. 9 shows the nitrogen content when the pressure at nitridation ischanged while setting the substrate temperature to 400° C. Under boththe low pressure (6.7 Pa) and the high pressure (67 Pa), the nitrogencontent was increases as the nitridation time was increased. Under thelow pressure, a larger amount of nitrogen was contained in the film.FIG. 3 shows the oxygen signal intensity when the pressure is changed.As the nitridation time was increased, the oxygen content was decreased.Under the low pressure, the oxygen content was significantly decreasedin the vicinity of 0.5 to 1.5 nm and this reveals that a displacementreaction between oxygen and nitrogen was generated. Under the highpressure, the oxygen was pushed out to the region thicker than 1.5 nmand this reveals that physical film thickness was increased.

FIG. 11 shows the nitrogen content when the temperature at nitridationis changed. At both the low temperature (250° C.) and the hightemperature (400° C.), the nitrogen content was increased as thenitridation time was increased.

FIG. 12 shows the oxygen content when the temperature is changed. Asdescribed above, the nitrogen content was the same between the processat low temperature for 40 seconds and the process at high temperaturefor 20 seconds, nevertheless, a great difference was generated in theoxygen content. This is considered because at the low temperature, areaction of displacing oxygen and nitrogen mainly occurred atnitridation, whereas at the high temperature, a reaction of cutting thebond between silicon and oxygen and immixing nitrogen mainly occurred.

From these, it is verified that when the nitridation treatment isapplied according to the present invention, an oxynitride film having adielectric constant higher than that of normal oxide film is formed.Also, as shown in FIGS. 9 and 11, the nitrogen concentration in film canbe freely controlled by changing the nitridation conditions and when thepresent invention is used, an oxynitride film having a nitrogenconcentration suited to the purpose can be formed.

Example 3

In this Example, the effect of preventing penetration of boron wasevaluated. FIG. 6 shows the results after the penetration degree ofboron in a P-type MOS capacitor is examined by SIMS. The sample used inFIG. 13 was using an N-type silicon substrate (phosphorus-doped) as thesilicon substrate and treated until the step (5) of Example 1.

In the SIMS analysis, a backside SIMS analysis method was used and thesputtering was performed with ion from the back surface (on thesubstrate side), because if the SIMS analysis is performed from thenormal front surface (on the gate electrode side), boron in the gateelectrode passes through the oxide film due to sputtering at theanalysis and reaches the substrate and the penetration of boron can behardly evaluated. The backside SIMS conditions used here were asfollows.

<Backside SIMS Conditions>

-   Measuring apparatus: CAMECA IMS-6f-   Primary ion species: O₂+-   Primary acceleration voltage: 3.0 KV-   Sputtering rate: about 0.2 nm/sec-   Measurement region: 30 μm-diameter circle-   Degree of vacuum: 3E-7 Pa or less-   Measured ion polarity: +-   Charge-up compensation process: not employed-   Interfering ion removal process: not employed

The signal intensity of ion was converted into the concentration withuse of a relative sensitivity factor (RSF) determined by measuring an Sistandard sample in which B was ion-injected. Also, the sputtering timewas converted into the depth by measuring the depth of a cratergenerated upon analysis with use of a surface roughness meter(DEKTAK3030 or DEKTAKS8000, manufactured by SLOAN). The precision ofdepth in the Si substrate depends on the stability of apparatus and isconsidered to be about ±10%, but in practice, the measurement isperformed from the substrate side of sample and the depth is inverted bydata processing, therefore, the absolute depth such as position ofinterface has no meaning.

As apparent from FIG. 13, boron (B) did not reach the substrate when thenitridation treatment was applied, and this reveals that the shifting orthe like of threshold voltage was prevented. Also, the Figure clearlyshows that when nitridation was not applied, boron was bled out from thegate electrode side at the annealing for activation and passed throughthe oxide film to reach the substrate. The P-type MOS transistor isoperated by applying a reverse bias to the channel on the substrate sideand thereby inducing pores, but the escape of boron causes decrease inthe resistance of polysilicon, as a result, a depletion layer may begenerated in the polysilicon electrode upon application of a reversebias and the electrical film thickness may be increased. However, asshown in the Figure, when the nitridation treatment was applied, boronis degenerated (piled up) on the oxynitride film surface and theabove-described deterioration of properties can be prevented.

INDUSTRIAL APPLICABILITY

As described in the foregoing pages, according to the present invention,an electronic device material comprising an oxynitride film havingexcellent properties and prevented from interface level at the interfacewith the substrate, and a production process thereof are provided.

1. A process for treating a substrate by plasma nitridation, comprising:providing the substrate having an oxide film thereon; and irradiatingplasma having an electron temperature of 0.5 to 2.0 eV on the oxide filmusing a mixed gas comprising argon gas and nitrogen gas to form anoxynitride film, wherein the plasma is irradiated on the oxide film at atemperature of 250 to 500° C. and under a pressure of 7 to 260 Pa, anitrogen atom content in the oxynitride film has a distribution suchthat the maximum value Ns of the nitrogen atom content in the oxynitridefilm at a surface of the oxynitride film opposite a surface facing thesubstrate is 10 to 40 atomic percent, and the maximum value Nb of thenitrogen atom content in the oxynitride film at the surface facing thesubstrate side is 0 to 10 atomic percent, the ratio Ns/Nb is 2 or more,and the oxynitride film has an electrical film thickness from 1.0 to 2.5nm.
 2. A process according to claim 1, wherein the plasma is generatedusing microwave irradiation by using a plane antenna member having aplurality of slots.
 3. A process according to claim 1, wherein the oxidefilm is formed by plasma processing or thermal oxidation.
 4. A processfor treating a substrate by plasma nitridation, comprising: forming anoxide film on the substrate; and irradiating plasma on the oxide filmusing a mixed gas comprising argon gas and nitrogen gas to form anoxynitride film, wherein the plasma is irradiated on the oxide film at atemperature of 250 to 500° C. and under a pressure of 7 to 260 Pa, anitrogen atom content in the oxynitride film has a distribution suchthat the maximum value Ns of the nitrogen atom content in the oxynitridefilm at a surface of the oxynitride film opposite a surface facing thesubstrate is 10 to 40 atomic percent, and the maximum value Nb of thenitrogen atom content in the oxynitride film at the surface facing thesubstrate side is 0 to 10 atomic percent, the ratio Ns/Nb is 2 or more,and the oxynitride film has an electrical film thickness from 1.0 to 2.5nm.
 5. A process according to claim 4, wherein the plasma is generatedusing microwave irradiation by using a plane antenna member having aplurality of slots.
 6. A process according to claim 4, wherein the ratioNs/Nb is 4 or more.
 7. A process for forming a gate oxynitride film,comprising: providing a substrate having an oxide film thereon; andirradiating plasma having density of 1×10¹⁰ to 5×10¹²/cm³ and anelectron temperature of 0.5 to 2.0 eV on the oxide film using a mixedgas comprising argon gas and nitrogen gas to form the oxynitride film,wherein the plasma is irradiated on the oxide film at a temperature of250 to 500° C. and under a pressure of 7 to 260 Pa, a nitrogen atomcontent in the oxynitride film has a distribution such that the maximumvalue Ns of the nitrogen atom content in the oxynitride film at asurface of the oxynitride film opposite a surface facing the substrateis 10 to 40 atomic percent, and the maximum value Nb of the nitrogenatom content in the oxynitride film at the surface facing the substrateside is 0 to 10 atomic percent, the ratio Ns/Nb is 2 or more, and theoxynitride film has an electrical film thickness from 1.0 to 2.5 nm. 8.A process according to claim 7, wherein the plasma is generated usingmicrowave irradiation by using a plane antenna member having a pluralityof slots.